CD24, a glycosylphosphatidylinositol-anchored molecule, is transiently expressed during the development of human central nervous system and is a marker of human neural cell lineage tumors

CD24 is a glycoprotein with an unusual structure consisting of a small protein core extensively glycosylated and linked to the outer surface of the plasma membrane by a glycosylphosphatidylinositol (GPI) lipid anchor. Its murine homolog mCD24 is transiently expressed during the development and differentiation of the hematopoietic and neural cell lineages. We have searched for the expression of CD24 in the developing and in the mature human brain as well as in a wide range of neuroectodermal tumors. Neuroblastomas, a subgroup of tumors able to maturate from undifferentiated features towards mature ganglioneuromas, were more extensively studied. Immunohistochemical studies demonstrated that CD24 is transiently expressed by neurons during human brain development. In neuroectodermal tumors, CD24 is a marker of neuronal tumors. Furthermore, in neuroblastomas, CD24 expression decreases as tumors differentiate. In non-neuronal neuroectodermal tumors, CD24 expression is mostly absent. When present, it correlates with the emergence of anaplastic histological features. Reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated the presence of an unique transcript identical in both hematopoietic, developing and tumoral nervous tissue. RT-PCR and in situ hydridization techniques showed that CD24 expression is transcriptionally regulated. Interestingly, Western blot analysis demonstrated differential CD24 isoforms according to the tissue (hematopoietic versus nervous), the differentiation status, and the origin of neuroblastomas likely reflecting variations in the extent of glycosylation. This indicates an additional level of regulation of CD24 involving post-translational modifications.